1. Field of the Invention
The present invention relates generally to lane keeping assistance system (also called, a lane following vehicle control system, but, hereinafter, is referred to the lane keeping assistance system) and method for an automotive vehicle. The present invention relates more particularly to a technical field of the lane keeping assistance system and method in which an automatic steering is carried out in such a way that a traffic lane information is retrieved during a vehicular run and a steering torque is given to a steering force transmission system to follow the vehicle along a traffic lane at a forward direction of the vehicle or a driver""s steering operation is supported to follow the traffic lane at the vehicular forward direction by providing a steering reaction torque is given to a vehicular steering force transmission system.
2. Description of the Related Art
In general, the lane keeping assistance system has a region in which the vehicle can autonomously run along a white line and in which a development force by an actuator does not give an influence on a steering intervention. Hence, it is necessary to reduce the development force by a control quickly if a driver""s steering intervention occurs.
On the other hand, in a system in which a gear direct drive power steering is used, a torque sensor mounted on a column shift of a steering wheel can directly be used to determine the driver""s steering intervention.
A Japanese Patent Application Publication No. Heisei 9-240502 published on Sep. 16, 1997 exemplifies a previously proposed lane keeping assistance system.
In the above-described Japanese Patent Application Publication, a torque sensor is installed to detect a steering torque from a vehicular driver in order to switch between an automatic steering and a manual steering by an accurate trap of an intention of the vehicular driver. When an output of the torque sensor is below a predetermined threshold value, a control mode is shifted into an automatic steering mode. When an output of the torque sensor is equal to or above the predetermined threshold value, the control mode is shifted into the manual steering mode.
However, an automotive industry has demanded the following requirements for the lane keeping assistance system.
That is to say, (1) Since a system cost becomes high with a correction for a drift of an output value of the torque sensor taken into consideration, the system cost is required to be reduced, and (2) Since it is necessary to make a part of a steering shift to which a steering torque is transmitted smaller in a diameter (torsion bar), a torsional rigidity of a steering system is reduced and a steering feeling thereof becomes worsened. Hence, the vehicular steering system is required to maintain its torsional rigidity and steering feeling thereof.
Therefore, it is, according to the requirements, difficult to mount the torque sensor in the steering system in terms of the steering performance and in terms of the cost. Then, in a case where such a direct driver""s steering intervention detecting device as described above is not present, a steering angle sensor (having a steering angular velocity output value) is used for a steering intervention determination.
However, it is possible for the steering angle sensor to detect the driver""s steering intervention only if a certain steering angular velocity occurs. Since the determination of the steering intervention in which no steering angular velocity is developed cannot be carried out, the determination of the steering intervention cannot be made in a case where a steady-state steering intervention (steering angular velocity ≈0xc2x0/S (zero degree per second)) is carried out.
Since the steering operations by the vehicular driver and by the steering control are interfered against each other, a large driver""s undesired feeling of the steering operation (a dull steering and a sticky feeling) occurs.
It is noted that the steady-state steering intervention (steering intervention without no generation of the steering angular velocity) is one of the following cases.
{circle around (1)} A case wherein the driver is running on or near to a boundary of the traffic lane (such lane markings as left and right white lines). For example, in a case wherein a large-sized truck is running on an adjacent traffic lane, the vehicle tends to run along a line deviated toward another traffic lane opposite to the adjacent traffic lane on which the truck is running. A case wherein the vehicle is running on the traffic lane near to which a cobble is present aside the traffic lane with a deviation thereof toward the traffic lane side opposite to the cobble.
{circle around (2)} A case wherein the vehicle is not running along the white lines but actually is running at a different side-road of the white lines. For example, a case wherein, during a vehicular run on a freeway, a guide-way or taxiway such as a guidance from a traffic lane in the freeway to a service area is brought over. In addition, the steering undesired feeling due to the steering interference is that, in a case of the manual steering intervention, a controlled output is caused to flow in a direction opposite to that caused by the driver""s intervention and undesired feelings of steering wheel""s weight increase and of a sticky feeling can be given to the driver.
It is, hence, an object of the present invention to provide lane keeping assistance system and method which can accurately determine such a steady-state steering intervention without generation of the steering intervention as described above and which can eliminate a large undesired feeling of steering due to a steering interference.
According to one aspect of the present invention, there is provided a lane keeping assistance system for an automotive vehicle, comprising: a traffic lane information detector (16) to detect an information related to a traffic lane on which the vehicle is about to run; a steering angle sensor (13) to detect a steering angle (xcex8) of a steering wheel of the vehicle; a steering position changing section (8, 9) by which the steering wheel of the vehicle is enabled to be displaced independently of a manual steering operation through the steering wheel; a controlled steering target value setting section (15, FIG. 12) that sets a controlled steering target value (xcex8*) when a controlled steering to follow the traffic lane is carried out on the basis of at least the traffic lane related information detected by the traffic lane information detector and the steering angle detected by the steering angle sensor; a controlled steering command value setting section (15, FIG. 20) that outputs a control command value (Iout) in accordance with the controlled steering target value; a control command value filtering section (15, 22 of FIG. 2, and 62 through 66 of FIG. 6) to filter the control command value to pass only frequency components of the control command value lower than a predetermined filter threshold value (fstr, fstr_low, fstr_mid, fstr_hi) to derive a filtered control command value (Iout_lpf_th) during an execution of the controlled steering; a manual steering intervention detector (15, 23 of FIG. 2, 67 and 69 of FIG. 6) to detect a steering intervention state to the controlled steering by the manual steering operation when the filtered control command value is in excess of a predetermined threshold control command value (Iout_lpf_th); and a controlled steering target value limiter (15, 24 and 25 of FIG. 2, and 70 and 71 of FIG. 6) to reduce the control command value (Iout) toward zero value to suppress the controlled steering target value toward a lower value direction including zero when the manual steering intervention is detected by the manual steering intervention detector.
According to another aspect of the present invention, there is provided a method applicable to a lane keeping assistance system for an automotive vehicle in which a control current is outputted to a motor (8) of an automatic steering actuator coupled to a vehicular steering system (3, 7) to provide a steering force thereto to follow the vehicle along a traffic lane on a road located in a vehicular forwarding direction during a vehicular run in an automatic steering mode, the method comprising: detecting (20 of FIG. 2 and 60 of FIG. 9) the control current (Iout) to be outputted to the motor during the automatic steering mode; providing (22 of FIG. 2, 62 through 66 of FIG. 6) a filter for the detected control current to pass only signal components of the detected control current whose frequencies are lower than a predetermined threshold frequency value of the filter to derive a filtered control current; determining (23 of FIG. 2 and 67 and 69 of FIG. 9) whether a manual steering intervention to the automatic steering occurs according to a magnitude of the filtered control current, the manual steering intervention being determined to occur depending on whether the magnitude of the filtered control current is in excess of a predetermined threshold current value of the filter; and reducing (24 and 25 of FIG. 2 and 70 and 71 of FIG. 6) the control current outputted to the motor toward zero value when, at the manual steering intervention determining step, the manual steering intervention is determined to occur according to a result of determination that the magnitude of the filtered control current (Iout_lpf) is in excess of the predetermined threshold current value (Iout_lpf_th).
This summary of the invention does not necessarily describe all necessary features so that the invention may also be a sub-combination of these described features.